The present invention relates to a resonant type switching power source capable of implementing zero-voltage switching on the basis of the resonance between an inductor and a capacitor and, more particularly, to a partial voltage resonant converter incorporated in such a switching power source.
A resonant type switching power source which can be controlled by a fixed frequency is studied. This type of switching power source has a partial voltage resonant converter which partially oscillates only on the turn-on and turn-off of the switches. A resonant converter of this kind promotes high frequency operations by reducing switching losses, allows parts which are not strictly resistive to high voltages to be used due to the voltage clamping characteristic, and frees the fixed frequency control from considerations which traditional voltage resonant converters should give to frequency control. A specific construction of the partial voltage resonant converter is disclosed in, for example, "Electronic Technologies", Nikkan Kogyo Shimbun, March 1990, pp. 30-37.
However, the problem with the conventional partial voltage resonant converter is that the inductor for realizing zero-voltage switching is constituted by a main transformer with windings, resulting in a complicated and expensive transformer. Another problem is that a main switch and an auxiliary switch cannot have their potentials matched due to the particular circuit arrangement, i.e., without resorting to an exclusive transformer for driving the auxiliary switch, further increasing the cost.